전산유체역학 해석을 통한 밀폐형 함정용 레이돔 내부 냉각장치 성능 예측

김원현(W. H. Kim),정의봉(E. B. Jeong),이승한(S. H. Lee),이재은(J. E. Lee),곽영찬(Y. C. Kwak) 한국정밀공학회 2018 한국정밀공학회 학술발표대회 논문집 Vol.2018 No.5월

다공배플 두께가 마이크로 연소기의 유동 및 혼합특성에 미치는 영향

김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.9

다공배플을 가진 마이크로연소기에 레이놀즈응력 난류모형을 이용하여 난류유동 및 혼합특성에 대한 수치해석 연구를 수행하였다. 다공배플은 연소실 내부에 다수의 3차원 와유동을 발생시키는 기하학적 특징을 가지고 있다. 그러한 형상특징 중에서 배플두께를 변화시킬 경우 와유동구조의 다양한 변화가 얻어졌다. 여러 와유동중에서 연료유동으로부터 생성된 와유동은 혼합도 증가에 결정적 역할을 하였다. 연소실 내부의 3차원 와유동구조는 배플두께 변화에 따른 유동의 발달상태에 의존하였다. 특히, 배플두께가 연료유입구 직경보다 작을수록 배플구멍 제트유동의 속도분포는 포물선형태에서 안장모양의 형태로 변하였다. 연소실내부의 재순환영역크기 및 혼합도는 이러한 제트유동구조에 밀접한 상관관계를 가졌다. Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle"s geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.

입구유동 가진이 있는 층류 후향계단 유동에서 열전달에 대한 프란틀수 효과해석

김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.9

입구유동 가진이 있는 층류 후향계단 유동에서 Pr수의 변화에 따른 열전달 특성변화를 조사하기 위하여 비정상 수치해석을 수행하였다. 입구는 가진주파수와 가진진폭의 변화에 따른 교란이 주어졌고, 온도함수의 물성치가 적용되었다. 열전달 변화에 대한 다양한 특징들이 열경계층 변화에 의해서 설명되 었다. 물성치가 일정한 경우와 비교하였을 때, 물성치가 온도의 함수성이 있는 경우  Pr < 1인 조건에서 열전달은 감소하였고, 반대로 Pr < 1인 조건에서 열전달은 증가하였다. 또한 가진진폭이 증가함에 따라 계단 후류 바닥면에서 열전달도 증가하였다. 그렇지만 가진주파수 변화의 경우 St < 0.2 조건에서 열전달이 크게 증가하는 특정주파수 영역이 존재하였다. 특히, 열전달의 증가는 재부착 길이의 rms값의 변동정도와 밀접한 관련이 있음을 보여주었다. The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.

골프 카트종류에 따른 에너지소비량 및 심박수 비교

김원현(Won-Hyun Kim),김민섭(Min-Sup Kim) 한국콘텐츠학회 2015 한국콘텐츠학회지 Vol.13 No.3

박용 중속 디젤 엔진 밸브트레인의 이상 소음 원인 규명

김원현(Won Hyun Kim),김훈석(Hoon Suk Kim),이수목(Soo Mok Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

An abnormal noise was detected in the valve train of newly developed medium speed diesel engine during the shop test. The valve train system and cam profiles were designed based on the kinetic and kinematic analyses. And the vibration characteristics of camshaft were also considered. Nevertheless, the impulse noise was generated and it was confirmed that this is due to the crashing of intake valve in closing timing at the initial test. To investigate the root causes, the dynamic behaviors of valve train system and the torsional vibration of camshaft were measured. From these experiments and the additional analysis, it was concluded that the one of the cause of crashing is coincidence of intake valve closing timing and the fuel cam timing. The other one is the maximum acceleration of intake cam which close to maximum operating speed of valve train. In this work, the intake cam profile was modified to reduce the maximum valve acceleration and then the abnormal noise was disappeared.

배플형 마이크로 연소기의 공기유입구 개수가 연소특성에 미치는 영향

김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국추진공학회 2019 한국추진공학회 학술대회논문집 Vol.2019 No.5

주당 운동참여 빈도와 일회 운동시 소요시간이 비만, 혈중지질 및 신장성장에 미치는 영향

김원현(Won Hyun Kim),김광희(Kwang Hoi Kim),김순기(Sun Gi Kim),김도윤(Do Youn Kim) 한국사회체육학회 2004 한국사회체육학회지 Vol.0 No.21

The effects on obese, cholesterol in blood and the height growth in accordance with the how frequency exercise in a week and the length of a one exercise. This research focused on obese students and aimed at analyzing what effects on change of lipid in blood, lipoprotein density and height growth in accordance with the frequency and the length of exercise. The result of this research is following. 1. The change in TC and lipid in blood, lipoprotein density caused a remarkable difference between two comparison group A group with people who exercise one or twice a week and people who never exercise, and the other group with people who exercise three or four time a week and people who exercise almost everyday. The change in TG caused a remarkable difference between male and female students(p<.05). It is also proved that the two comparison group differ ; A group with people who never exercise and people who exercise one or twice a week and the other group with people who exercise one or twice a week and people who exercise almost everyday. There also is a meaningful difference of HDL-C between male and female students.(p<.05) However, there wasn`t any considerable difference between male and female students(p<.05) In addition, it was shown that change in VLDL lead to a meaningful difference in both comparison group. The variance of height growth caused a remarkable difference between male and female students(p<.05). It is also proved that the two comparison group differ; A group with people who never exercise and people who exercise one or twice a week and the other group with people who exercise three or four time a week and people who exercise almost everyday. 2. As a result of a length of exercise, There wasn`t any considerable difference between male and female students(p<.05) But, there is a considerable difference between male and female students(p<.05) There is a meaningful variance of HDL-C between male and female student(p<.05). However, there wasn`t any considerable difference between male and female students(p<.05) There is A regardful variance of VLDL between male and female student(p<.05). There is also a meaningfuldifference of the height growth between male and female student(p<.05). According to the result of our research, a regular exercise attendance has a positive effect on in blood, lipoprotein density. However, when viewed in the perspective of the lengh of exercise, in blood, lipoprotein density tended to show a negative effect to some extent. Height growth showed a meaningful gap in accordance with the frequency and the length of exercise. However, it can`t be said that exercise influences, the growth of students` height, because it is not easy to apprehend the effect of exercise upon growth without thoroughly controlling the synthetically interacting caloric intake, internal secretion, the form and the intensity of exercise, and inherited attribute. Since this paper focused on analyzing obese students, a systematic research, which can fully explain the time-serial phase of individual development, is to be done by conducting comparative and cross-boundary researches between the obese and the normal

Java Media Framework을 이용한 웹 기반 실시간 멀티미디어 스트림 전송의 설계 및 구현

김원현(Won-Hyun Kim),김윤호(Yun-Ho Kim) 한국멀티미디어학회 2000 한국멀티미디어학회 학술발표논문집 Vol.2000 No.2

원형/비원형 난류 제트 유동의 혼합 특성 변화에 대한 수치 해석 연구

김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2020 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.8 No.1

난류 제트 유동에서 입구 노즐 단면 형상 변화에 따른 혼합 특성 변화를 살펴보기 위해 레이놀즈 응력 모형(RSM)을 사용한 수치 해석을 수행하였다. 유동 혼합에 대한 형상 효과를 분석하기 위해, 원형 노즐과 동일한 입구 단면적을 가지는 정사각형과 정삼각형의 비원형 제트를 선택하였다. 원형 및 비원형 제트에 대해 축 방향 속도, 와유동 크기, 혼합도, 정압 및 난류 강도 변화를 통해 입구 노즐의 형상 변화가 혼합 특성에 미치는 영향을 살펴보았다. 그러한 결과로부터, 원형 제트에 비해 비원형 제트의 혼합 성능이 크게 향상되었고, 정사각형 제트보다 정삼각형 제트에 대해 상대적으로 높은 혼합성능을 얻을 수 있음을 확인하였다. Numerical analysis using Reynolds stress model (RSM) are performed to examine the variation of mixing characteristics according to the change in cross-sectional shape of nozzle inlet in turbulent jets. To analyze the geometric effects on the flow mixing, non-circular jets of square and equilateral triangular shapes having the inlet area of the same magnitude as the circular jet are selected. For the circular and noncircular jets, the shape effect of nozzle inlet on the mixing characteristics is investigated by the variations of axial velocity, vorticity magnitude, mixedness, static pressure and turbulence intensity. From such results, it is confirmed that the mixing performance of the non-circular jet is significantly improved in comparison of the circular jet, and relatively higher mixing performance is obtained for the equilateral triangular jet than the square jet.

육상용 중속 디젤엔진 발전기세트의 진동 특성 및 저감

김원현(Won-Hyun Kim),정건화(Kun-Hwa Jung),이수목(Soo-Mok Lee),류영석(Young-Seok Ryoo) 한국마린엔지니어링학회 2006 한국마린엔지니어링학회 학술대회 논문집 Vol.2006 No.-

Diesel power plant(DPP) with the medium speed diesel engine is operated under the very severe condition in aspect of load and operating time as compared with the marine diesel generator set. So, minimized vibration level have to be insured for the more stable operation of engine and generator. The vibration of generator set mainly comes from the resonance between the rigid modes by resilient mount or distortion modes by structural stiffness and the excitation forces of engine. Then, avoidance of resonance with structural modification is generally well known. In this paper, the first order vibration in non-resonance range and local vibration modes were investigated by impact test, response /ODS(operational deflection shape) measurement and 3D finite element analysis for the additional reduction of vibration. The proposed countermeasures were actually applied and their final effects were verified through the in-situ measurement.